Technical Field
The present disclosure relates to a converter circuit. More particularly, the present disclosure relates to a converter circuit with a switchable topology.
Description of Related Art
A conventional power system includes a first converter and a second converter connected in cascade. For example, the first converter is an AC-to-DC converter, and the second converter can be a point of load (POL). An AC power is transformed by the AC-to-DC converter, and then the transformed DC power is further converted by multiple POLs into lower DC voltages for various electronic devices.
For satisfying optimal requirement of the system performance or decreasing system loss, in some specific conditions (e.g., small power condition), the system regulates the output of the AC-to-DC converter to a lower level, so as to improve efficiency of the POL corresponding to the second converter, but the output of the AC-to-DC converter is not regulated to be too low, to further maintain the high efficiency of the entire system.
For example, when the system operates with a heavier load (e.g., the output is provided for a load between a half load and a full load), the output of the AC-to-DC converter is 12 Volts; when the system operates with a lighter load (e.g., the output current is smaller), the efficiency of the POL corresponding to the second converter would decrease if the output of the AC-to-DC converter is maintained 12 Volts, such that the efficiency of the entire system decreases accordingly. If, at the moment, the output of the AC-to-DC converter is decreased, for example, to be 6 Volts, then the efficiency of the POL corresponding to the second converter would increase. As a result, by changing the output of the AC-to-DC converter at different states, the efficiency of the entire system is higher compared to the approach of maintaining the output of the AC-to-DC converter, although its efficiency would change accordingly (e.g., the efficiency of the converter would decrease when the output of the AC-to-DC converter is decreased). In addition, in some applications, e.g., a charging system of an electric car, it requires that its converter generate different output voltages in different situations because, for different electric cars, model numbers of batteries are different and thus their charging voltages are different. As a result, for satisfying charging demands of various electric cars, output voltages of present charging equipments usually have a broader range (e.g., 150 V-450 V), so as to meet the demands of the aforementioned applications by changing the output of the converter.
For a pulse width modulation (PWM) converter, the gain of the converter can be decreased by decreasing the output voltage, and for example, decreasing the output voltage can be realized by reducing the duty cycle of the switches in the converter. For a resonant converter, the gain of the converter can be decreased by changing the operating frequency of the switches in the converter. For a series resonant circuit, e.g., a LLC series resonant converter, increasing the operating frequency can decrease the gain.
However, regardless of the type of the converter topology, the decreased gain usually corresponds to an increase of circuit loss and an efficiency decrease of the converter. Therefore, even if the post-stage converter has an enhanced efficiency due to the decrease of the output voltage of the previous-stage converter, the efficiency of the entire system still cannot be significantly improved.